Systemic lupus erythematosus is a multisystem autoimmune disorder of unknown etiology and poorly understood pathogenesis. The heterogeneity of lupus makes it especially difficult to characterize and quantitate in either routine clinical care or in the setting of controlled clinical trials. These problems limit clinical studies of new therapeutic approaches. We propose to apply methods to analyze gene expression using microarrays to characterize patients with lupus with the following specific aims: 1. To compare 7 lupus patients and 3 control subjects for differences in gene expression on gene filter microarrays analyzing 20,000-30,000 gene sequences. 2. To further evaluate groups of related genes suggested by Aim #1 to be of importance in lupus using either selected microarays or RNA (Northern) blot analyses. 3. To examine the gene expression findings for correlations with clinical features, activity and severity of lupus. Studies of gene expression in subjects with lupus offer several advantages over existing approaches. In addition to providing a noninvasive, easily repeatable measure of immune system activation, the results can be quantified and compared for many subjects. More importantly, there is the real possibility of identifying new pathways of immune activation at the molecular level which may in turn suggest approaches to the development of novel therapeutic agents.